This application is based on application No. 11-223669 filed in Japan, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a sheet trailing edge restriction member which is applicable to sheet feeder trays and sheet cassettes of image forming apparatuses such as copying machines, facsimile machines and printers.
2. Description of Related Art
Image forming apparatuses generally have a sheet holding member called xe2x80x9csheet trayxe2x80x9d, xe2x80x9csheet feeder cassettexe2x80x9d or xe2x80x9csheet cassettexe2x80x9d (hereinafter referred to generally as xe2x80x9csheet cassettexe2x80x9d). Most of modern sheet cassettes are adapted to accommodate a great number of sheets, for example, 500 sheets.
The sheets are fed out of the sheet cassette one by one in order from the top. For prevention of feed-out of plural sheets at a time, the sheet cassette is provided with separation claws. The separation claws project on the sheet stack to catch opposite ends of an upper front edge of the sheet stack.
The sheet cassette further has a bias plate which is adapted to bias a front portion of the sheet stack upward in the sheet cassette to lift the front portion of the sheet stack. Therefore, the sheet stack is lifted by the bias plate with the opposite ends of the upper front edge thereof caught by the separation claws.
Where a great number of sheets (e.g., 500 sheets) are accommodated in the sheet cassette, the sheet stack P is not lifted by the bias plate 63 as shown in FIG. 6A. As the thickness of the sheet stack P is reduced with a reduced number of sheets held in the sheet cassette, the bias plate 63 lifts the front portion of the sheet stack P to a higher level to press the front upper portion of the sheet stack against the separation claws 66 as shown in FIG. 6B. Therefore, the sheet stack P should be supported at its rear end with the front portion thereof being lifted.
Where the sheet cassette is adapted to accommodate an increased number of sheets, the weight of the sheet stack held in the sheet cassette is increased. Therefore, a restriction member 30 for positioning the trailing edges of the sheets should firmly be fixed upright on a bottom face 31 of the sheet cassette so as not to be disengaged from the bottom face 31. On the other hand, the sheet trailing edge restriction member 30 should be mountable at different positions in the sheet cassette depending on the size of the sheets. Therefore, the sheet trailing edge restriction member 30 is preferably constructed such that its mounting position can easily be changed.
That is, the sheet trailing edge restriction member 30 preferably has such a construction that its mounting position can easily be changed and, once it is mounted in position, it can assuredly support the rear end of the stack P of a great number of sheets held in the sheet cassette without easily disengaging therefrom.
In view of the technical background described above, it is an object of the invention to provide a sheet trailing edge restriction member which is capable of assuredly supporting a rear end of a sheet stack held in a sheet holder, and to provide a sheet holder having such a sheet trailing edge restriction member.
It is another object of the invention to provide a sheet trailing edge restriction member which can easily be attached to and detached from a sheet holder and, once it is mounted in the sheet holder, can assuredly support a sheet stack held in the sheet holder without disengagement thereof.
In accordance with the present invention, there is provided a sheet holder which comprises a sheet holding portion and a restriction member mounted in a predetermined position of the sheet holding portion for positioning a rear end of a sheet stack held in the sheet holding portion. The restriction member comprises: a main body disposed upright in the sheet holding portion; a hook extending alongside the main body with a predetermined space defined therebetween for fixing the main body to the sheet holding portion, the hook being deformable toward the main body (toward the space) so as to be brought into and out of engagement with the sheet holding portion; a rear support plate forwardly displaceable from the main body so that, when the sheet stack has a greater thickness with a greater number of sheets held in the sheet holding portion, the rear support plate is pressed against the main body by the rear end of the sheet stack thereby to be substantially flush with the main body and, as the number of the sheets is reduced, the rear support plate is displaced forward from the main body to support the rear end of the sheet stack; and an insert projecting from the rear support plate to be inserted in the space between the main body and the hook, the insert being movable in accordance with the displacement of the rear support plate so as to be brought out of the space when the rear support plate is displaced to a forward terminal position.
With this arrangement, when the insert is inserted in the space between the main body and the hook of the restricting member, the hook cannot be deformed toward the main body. This is because the hook can be deformed toward the main body only when the predetermined space is present between the hook and the main body. When the space is blocked by inserting the insert in the space, the hook cannot be deformed.
Since the main body is disposed upright in the sheet holding portion and the hook is not allowed to be deformed in engagement with the sheet holding portion, the main body, i.e., the sheet trailing edge restriction member will not be disengaged from the sheet holder.
In the present invention, the insert to be inserted in the space is integral with the rear support plate, and shifted between a state where the insert is inserted in the space and a state where the insert is out of the space in accordance with the displacement of the rear support plate for switching the hook between a deformable state and a nondeformable state. More specifically, when the sheet stack has a greater thickness with a greater number of sheets being held in the sheet holding portion, the rear support plate is substantially flush with the main body. At this time, the insert is inserted in the space between the main body and the hook. Even if the sheet stack having a greater thickness exerts a force on the main body by gravity with its rear end contacting the main body in this state, the hook is prevented from being deformed and disengaged from the sheet holding portion. Therefore, the sheet trailing edge restriction member is not disengaged from the sheet holding portion.
When the rear support plate is displaced to the forward terminal position, the insert is withdrawn from the space, so that a user can deform the hook toward the main body. Thus, the user can detach the sheet trailing edge restriction member from the sheet holding portion, and easily change the mounting position of the restriction member.
In the sheet trailing edge restriction member which can easily be attached to and detached from the sheet holding portion by deforming the fixing hook toward the space, the hook is not allowed to be deformed with the space blocked by the insert to prevent the restriction member from being disengaged from the sheet holding portion. The insert to be inserted in the space is integral with the rear support plate thereby to be movable in association with the rear support plate. Therefore, even when a greater number of sheets are held in the sheet holding portion, the hook is not deformed, so that the sheet trailing edge restriction member is not disengaged from the sheet holding member.
Further, the rear support plate and the insert are not separate components but the sheet trailing edge restriction member is constructed as a unitary member. Therefore, there is no possibility that any components of the restriction member become missing due to frequent positional change of the restriction member.
One embodiment of the present invention will hereinafter be described in detail with reference to the attached drawings.